PROJECT SUMMAY/ABSTRACT This is an application for an NIH R01 Research Project Grant. Our long-term goal is to determine how Mycobacterium tuberculosis (Mtb) disrupts the host immune response to establish infection in humans, and to use this information to develop better vaccines and therapies for tuberculosis (TB). In our prior work, we used proteomics to systematically define the interactions between secreted Mtb proteins and human proteins, and discovered a network of several hundred highly-specific interactions that potentially play important roles in Mtb pathogenesis and host defense. We began an initial genetic analysis of the interaction network, and discovered both a novel virulence factor LpqN, as well as its probable host target, the ubiquitin ligase CBL. The specific goal of this application is to study the mechanisms by which CBL regulates innate immune signaling in macrophages and in mice. In Aim 1 we will use biochemical analyses to test the hypothesis that CBL ubiquitylates IRF3 and/or IRF7, targeting them for degradation and thus suppressing antiviral responses. If this hypothesis is incorrect we will take more global approaches to identifying CBL substrates. In Aim 2 we will determine the mechanism by which the virulence factor LpqN disrupts CBL function to promote Mtb growth. In Aim 3 we will explore the function of a novel phosphorylation event we have identified on serine 450 of CBL. These findings will pave the way for future studies that will seek to uncover the molecular mechanisms by which these host factors contribute to immunity and may suggest ways that the factors can be manipulated for therapeutic benefit.